Invasive flow measurement devices, such as orifice plates affect the flow itself. Measurement without orifice plate, or other restrictions applied for direct flow measurement, is particularly important in very low pressure systems where even the 1 to 5 psi pressure drop across an orifice cannot be tolerated. Such parameters are increasingly common in the flow produced from shallow gas wells and coal bed methane fields.
Flow measurement using non-invasive acoustic characteristics of the fluid flowing therethrough are known. Active systems are known whereby ultrasonic frequency and the like are transmitted into the system and acoustic responses received which are analyzed for flow including U.S. Pat. No. 6,672,131 to Aldal et al. Others implement a combination of non-invasive vibrational response and flow coupled pressure measurement to ascertain flow such as U.S. Pat. No. 5,415,048 to Diatschenko. The systems are characterized by instrumentation and processing components which are high power consumers, conventional in that they typically require connection to existing utility services.
Other considerations are that sensors are unreliable in their repeatability due to methods and apparatus for mounting. Conventional microphones require electronic amplification which introduces signal to noise considerations and require non-trivial power sources unsuitable for remote locations isolated from utilities. Conventional data collection requires significant power and transmission of raw data requires large bandwidth and sophisticated communications.
There is a demonstrated need for flow measurement capabilities such as in remote, un-serviced locations.